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LUX-ZEPLIN (LZ), a second generation dark matter experiment, got a big boost when the Department of Energy and National Science Foundation selected it as one of three experiments that will be funded in the next-generation dark matter search. LZ will build on the Large Underground Xenon (LUX) experiment, which has been operating at the 4850 Level of the Sanford Underground Research Facility since 2012, and on the ZEPLIN dark matter program in the United Kingdom, which pioneered the use of these types of detectors underground.

“We emerged from a very intense competition,” said Daniel McKinsey, professor of physics at Yale and a spokesperson for LUX. “We have the most sensitive detector in the world, with LUX. LZ will be hundreds of times more sensitive. It’s gratifying to see that our approach is being validated.”

Construction on the supersized detector is scheduled to begin in 2016, with a commissioning date of 2018. Plans for LZ have been in the works for several years.

“This is great news for the future of Dark Matter exploration and the Sanford Lab,” said Mike Headley, Executive Director of the South Dakota Science and Technology Authority. “The LZ experiment will play a key role in the future of the lab and we’re pleased that the DOE selected the experiment. It certainly will extend the state’s investment in this world-class facility.”

Rick Gaitskell, Hazard Professor of Physics at Brown, is a founding member of LZ and also co-spokesperson for the LUX experiment.

“The go-ahead from DOE and NSF is a major event,” Gaitskell said. “The LZ experiment will continue the liquid xenon direct dark matter search program at Sanford Lab, which we started with the operation of LUX in 2013. LUX will run until 2016 when we will replace it with LZ, which can provide a further improvement in sensitivity of two orders of magnitude due to its significant increase in size.”

Even if LUX makes a dark matter detection before LZ is up and running, LZ will still be necessary to confirm the detection and fully characterize the nature of WIMPS, Gaitskell said.

“This green light is a clear indication of the value the agencies see, not only in all the preparatory work that has gone into LZ, but also in the existing accomplishment of LUX and Sanford Lab these past few years,” said Simon Fiorucci, a research scientist at Brown who is the science coordinator for LUX and simulations coordinator for LZ. “LZ will be timed so that it is ready to start operations when LUX delivers its final results and reaches the limits of its technology. It will be a very natural transition.”

Harry Nelson, professor of physics at the University of California, Santa Barbara and spokesperson for the LZ Collaboration, said, “We still have a lot of work to do. Basically, we got the green light to go the next green light, then the next green light.” Still, he continued, “Everyone is excited.”

About us.
The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s. In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

The quest to find the most mysterious particles in the Universe is entering a critical phase, scientists say.

An experiment located in the bottom of a gold mine in South Dakota, US, could offer the best chance yet of detecting dark matter.

Scientists believe this substance makes up more than a quarter of the cosmos, yet no-one has ever seen it directly.

Early results from this detector, which is called LUX, confirmed it was the most powerful experiment of its kind.

In the coming weeks, it will begin a 300-day-long run that could provide the first direct evidence of these enigmatic particles.

Spotting WIMPs

Beneath the snow-covered Black Hills of South Dakota, a cage rattles and creaks as it begins to descend into the darkness.

For more than 100 years, this was the daily commute for the Homestake miners searching for gold buried deep in the rocks.

Today, the subterranean caverns and tunnels have been transformed into a high-tech physics laboratory.

Scientists now make the 1.5km (1-mile) journey underground in an attempt to solve one of the biggest mysteries in science.

“We’ve moved into the 21st Century, and we still do not know what most of the matter in the Universe is made of,” says Prof Rick Gaitskell, from Brown University in Rhode Island, one of the principle investigators on Large Underground Xenon (LUX) experiment.

The LUX detector is located 3km underground – and could be our best hope yet of finding dark matter

Scientists believe all of the matter we can see – planets, stars, dust and so on – only makes up a tiny fraction of what is actually out there.

They say about 85% of the matter in the Universe is actually dark matter, so called because it cannot be seen directly and nobody really knows what it is.

This has not stopped physicists coming up with ideas though. And the most widely supported theory is that dark matter takes the form of Weakly Interacting Massive Particles, or WIMPs.

Prof Gaitskell explains: “If one considers the Big Bang, 14bn years ago, the Universe was very much hotter than it is today and created an enormous number of particles.

“The hypothesis we are working with at the moment is that a WIMP was the relic left-over from the Big Bang, and in fact dominates over the regular material you and I are made of.”

The Homestake gold mine, which has now been converted into a lab, is in the Black Hills of South Dakota

The presence of dark matter was first inferred because of its effect on galaxies like our own.

As these celestial systems rotate around their dense centre, all of the regular matter that they contain does not have enough mass to account for the gravity needed to hold everything together. Really, a spinning galaxy should fly apart.

It is so pervasive throughout the Universe that researchers believe a vast number of WIMPs are streaming through the Earth every single second. Almost all pass through without a trace.

However, on very rare occasions, it is thought that dark matter particles do bump into regular matter – and it is this weak interaction that scientists are hoping to see.

The LUX detector is one of a number of physics experiments based in the Sanford Underground Research Facility that require a “cosmic quietness”.

Prof Gaitskell says: “The purpose of the mile of rock above is to deal with cosmic rays. These are high-energy particles generated from outside our Solar System and also by the Sun itself, and these are very penetrating.

“If we don’t put a mile of rock between us and space, we wouldn’t be able to do this experiment.”

Inside a cavern in the mine, the detector is situated inside a stainless steel tank that is two storeys high.

The detector is in housed in a tank that is filled with purified water

This is filled with about 300,000 litres (70,000 gallons) of ultra-purified water, which means it is free from traces of naturally occurring radioactive elements that could also interfere with the results.

“With LUX, we’ve worked extremely hard to make this the quietest verified place in the world,” says Prof Gaitskell.

At the detector’s heart is 370kg (815lb) of liquid xenon. This element has the unusual, but very useful, property of throwing out a flash of light when particles bump into it.

And detecting a series of these bright sparks could mean that dark matter has been found.

The LUX detector was first turned on last year for a 90-day test run. No dark matter was seen, but the results concluded that it was the most sensitive experiment of its kind.

Now, when the experiment is run for 300 days, Prof Gaitskell says these interactions might be detected once a month or every few months.

The team would have to see a significant number of interactions – between five and 10 – to suggest that dark matter has really been glimpsed. The more that are seen, the more statistical confidence there will be.
LUX uses light detectors called photomultiplier tubes to record any flashes of light

However, LUX is not the only experiment setting its sights on dark matter.

With the Large Hadron Collider, scientists are attempting to create dark matter as they smash particles together, and in space, telescopes are searching for the debris left behind as dark matter particles crash into each other.

LHC at CERN

Mike Headley, director of the South Dakota Science and Technology Authority, which runs the Sanford laboratory, says a Nobel prize will very probably be in store for the scientists who first detect dark matter.

He says: “There are a handful of experiments located at different underground laboratories around the world that want to be the first ones to stand up and say ‘we have discovered it’, and so it is very competitive.”

Finding dark matter would transform our understanding of the Universe, and usher in a new era in fundamental physics.

However, there is also a chance that it might not be spotted – and the theory of dark matter is wrong.

Dr Jim Dobson, based at the UK’s University of Edinburgh and affiliated with University College London, says: “We are going into unknown territory. We really don’t know what we’re going to find.

“If we search with this experiment and then the next experiment, LUX Zeppelin, which is this much, much bigger version of LUX – if we didn’t find anything then there would be a good chance it didn’t exist.

He adds: “In some ways, showing that there was no dark matter would be a more interesting result than if there was. But, personally, I would rather we found some.”

Prof Carlos Frenk, a cosmologist from Durham University, says that many scientists have gambled decades of research on finding dark matter.

He adds: “If I was a betting man, I think LUX is the frontrunner. It has the sensitivity we need. Now, we just need the data.

“If they don’t [find it], it means the dark matter is not what we think it is. It would mean I have wasted my whole scientific career – everything I have done is based on the hypothesis that the Universe is made of dark matter. It would mean we had better look for something else.”

After its first run of more than three months, operating a mile underground in the Black Hills of South Dakota, a new experiment named LUX has proven itself the most sensitive dark matter detector in the world.

LUX researchers, seen here in a clean room on the surface at the Sanford Lab, work on the interior of the detector, before it is inserted into its titanium cryostat.

Photomultiplier tubes capable of detecting as little as a single photon of light line the top and bottom of the LUX dark matter detector. They will record the position and intensity of collisions between dark matter particles and xenon nuclei.

“LUX is blazing the path to illuminate the nature of dark matter,” says Brown University physicist Rick Gaitskell, co-spokesperson for LUX with physicist Dan McKinsey of Yale University. LUX stands for Large Underground Xenon experiment.

Three researchers from Lawrence Livermore National Laboratory — principal investigator Adam Bernstein and staff scientists Peter Sorensen and Kareem Kazkaz, all from the Lab’s Rare Event Detection Group in Physics Division — have been closely involved with the LUX project since its inception.

Dark matter, so far observed only by its gravitational effects on galaxies and clusters of galaxies, is the predominant form of matter in the universe. Weakly interacting massive particles, or WIMPs – so-called because they rarely interact with ordinary matter except through gravity — are the leading theoretical candidates for dark matter. The mass of WIMPs is unknown, but theories and results from other experiments suggest a number of possibilities.

LUX has a peak sensitivity at a WIMP mass of 33 GeV/c2 (see **below), with a sensitivity limit three times better than any previous experiment. LUX also has a sensitivity that is more than 20 times better than previous experiments for low-mass WIMPs, whose possible detection has been suggested by other experiments. Three candidate low-mass WIMP events recently reported in ultra-cold silicon detectors would have produced more than 1,600 events in LUX’s much larger detector, or one every 80 minutes in the recent run. No such signals were seen.

“This is only the beginning for LUX,” McKinsey said. “Now that we understand the instrument and its backgrounds, we will continue to take data, testing for more and more elusive candidates for dark matter.”

“Lawrence Livermore National Laboratory researchers are making key contributions to a physics experiment that will look for one of nature’s most elusive particles, ‘dark matter,’ using a tank nearly a mile underground beneath the Black Hills of South Dakota.

Shown is a side view of the Lawrence Livermore National Laboratory-designed and built copper photomultiplier tube mounting structure, which is a key component of the Large
Underground Xenon (LUX) detector, located at the Sanford Underground Research Facility in Lead, S.D. No image credit.

The Large Underground Xenon (LUX) experiment located at the Sanford Underground Research Facility in Lead, S.D. is the most sensitive detector of its kind to look for dark matter. Thought to comprise more than 80 percent of the mass of the universe, scientists believe dark matter could hold the key to answering some of the most challenging questions facing physicists in the 21st century. So far, however, dark matter has eluded direct detection.

LLNL researchers have been involved in the LUX experiment since 2008.

‘We at LLNL initially got involved in LUX because of the natural technological overlap with our own nonproliferation detector development programs,’ said Adam Bernstein, who leads the Advanced Detectors Group in LLNL’s Physics Division.

‘It’s very exciting to reflect that as a result, we are now part of a world-class team that stands an excellent chance of being the first to directly and unambiguously measure cosmological dark matter particle interactions in an earthly detector.'”

Almost a mile underground, in a new science facility in South Dakota, scientists of the LUX collaboration are building the world’s largest dark-matter search experiment.

“This summer, researchers working in a former gold mine in South Dakota will slowly lower a titanium thermos the size of a phone booth into a large tank of purified water. The cylindrical thermos—nicknamed the can by its inventors—will hold ultra-pure liquid xenon and an array of photosensors, each capable of sensing a single photon of light.

The can will be the core component of the Large Underground Xenon detector, or LUX, the most sensitive experiment yet to search for the elusive substance called dark matter.